Dielectric effects on the ion distribution near a Janus colloid

Abstract

Spherical Janus colloids, particles with different surface properties on their two hemispheres, are generally heterogeneous in permittivity. This dielectric heterogeneity may affect their behavior in electrolytes and external electric fields, but is typically not taken into account in computational studies. We apply the iterative dielectric solver developed by Barros and Luijten [Phys. Rev. Lett., 2014, 113, 017801] in combination with preconditioning techniques that can accurately and efficiently compute the polarization of dielectrically anisotropic particles. Employing this approach, we systematically study the ion distribution around neutral and charged Janus particles with various permittivities, immersed in symmetric and asymmetric electrolytes. We demonstrate that neutral Janus colloids may carry a nonzero dipole moment in asymmetric salts. For charged Janus colloids, dielectric effects can substantially influence the electric double layer. These findings also have implications for other dielectrically anisotropic entities, such as proteins.

Asymmetric electrolytes near structured dielectric interfaces

“…In this paper, we apply the iterative dielectric solver (IDS), a recently developed fast BEM-based dielectric algorithm optimized for MD simulations, 34,35 that has been demonstrated to be competitive to imagebased methods, 36 to study the structured interfaces. The IDS has been applied to study complicated dielectric geometries such as patchy colloids 37,38 and self-assembly in binary suspensions. 33 The surface structures that are of interest have nanoscale dimensions, making first-principle or all-atom simulations infeasible.…”

Dielectric Effects on Ion Transport in Polyelectrolyte Brushes

“…Furthermore, earlier calculations have predicted nanopore permittivity to alter number, − distribution, and even type of ions within the channel through, for example, full dielectric exclusion of ions or enhancement of ion selectivity . Yet, even though the materials used as PEB substrate range from insulating , to conducting , (even a thin metallic coating is sufficient to alter the substrate properties), the effect of substrate permittivity on PEBs remains an open question, apart from a study of PE-grafted silica nanoparticles …”

Accurate and efficient numerical simulation of dielectrically anisotropic particles

“…Thus, polarization effects are ignored altogether in many simulation models. Recent studies have demonstrated that this is not generally justified, since dielectric effects can significantly alter the ionic density profile near a surface, [6][7][8][9][10][11] modulate ion mobility, 12 and affect the structure of self-assembled aggregates. 13 Until now, these studies have only addressed dielectrically isotropic particles.…”

“…To clarify these issues in the case of dielectrically heterogeneous particles, where additional dielectric interfaces arise, we consider the prototypical example of a Janus sphere com-prised of a silica hemisphere and a metallic hemisphere. 10 This example exhibits three dielectric interfaces: two hemispherical surfaces and one equatorial disk (Fig. 4).…”

“…Intuitively, this preconditioning remedies the disproportionate weight of patches with large prefactors in Eq. (10), i.e., large εi and ∆ε i in the residual-precisely the situation that arises if multiple dielectric mismatches are present. This method of preconditioning can be implemented in a particularly simple manner, namely in each iteration of GMRES the residual of the ith patch is normalized by εii .…”